Analog Devices Inc./Maxim Integrated MAX6138BEXR50

Overview

MAX6138BEXR50 from Maxim Integrated is a precision two-terminal shunt-mode bandgap voltage reference with a fixed 5.000V reverse breakdown voltage, 0.2% initial accuracy, and 25ppm/°C max temperature coefficient over –40°C to +85°C. It operates across a wide shunt current range (60µA to 15mA), delivers low 80µVRMS wideband noise (10Hz–10kHz), and requires no external output capacitor - enabling stable operation with capacitive loads in space-constrained analog signal chains.

For engineers reviewing the MAX6138BEXR50 datasheet, MAX6138BEXR50 pinout, MAX6138BEXR50 application, or MAX6138BEXR50 equivalent, key selection criteria include its SC70-3 package footprint, guaranteed long-term stability (120ppm at 1000h), low dynamic impedance (0.5–1.1Ω), and compatibility with high-precision ADC/DAC biasing, portable power monitoring, and industrial sensor excitation circuits.

Technical Context

The MAX6138BEXR50 implements a laser-trimmed BiCMOS bandgap core to achieve tight initial tolerance and low thermal drift. Its two-terminal architecture functions as a programmable current sink, regulating voltage by dynamically adjusting shunt current to maintain 5.000V across terminals under varying load and supply conditions.

It features guaranteed performance across –40°C to +85°C without external compensation, supports capacitive loads up to ≥1µF, and exhibits minimal reverse voltage change (3.5–12.0mV) over 1–15mA shunt current variation - critical for maintaining reference integrity in battery-powered and thermally variable systems.

Key Specifications

Pinout & Package

MAX6138BEXR50 is housed in a 3-pin SC70-3 surface-mount package (1.8mm × 1.8mm × 0.9mm), occupying 50% less board area than comparable SOT23-3 references. Pin 3 is NC and must be left floating or tied to Pin 2 per datasheet requirement.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar shunt voltage reference applications.

Compared with TLVH431ACDBVR and LM4040C50IDCKR, MAX6138BEXR50 offers superior initial accuracy (0.2% vs. 0.5–1.0%), lower temperature coefficient (25ppm/°C vs. 100ppm/°C), and lower noise (80µVRMS vs. >120µVRMS), making it optimal for high-resolution data acquisition where reference-induced error must be minimized.

Availability

MAX6138BEXR50 is available at Aetrix Electronics and suitable for portable medical sensors, industrial process transmitters, and handheld test equipment requiring stable component supply, consistent parametric performance, and long-term availability assurance.

Supply support for MAX6138BEXR50 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for demanding industrial, medical, and communications applications.

The MAX6138 family was developed to deliver high-accuracy, low-noise, space-efficient shunt references for battery-powered and thermally variable systems - directly addressing limitations of legacy devices like the LM4040 in modern compact instrumentation.

FAQ

What is the maximum shunt current rating for MAX6138BEXR50 before risking damage?

The absolute maximum reverse current for MAX6138BEXR50 is 20mA, as specified in the Absolute Maximum Ratings table. Continuous operation above 15mA is not recommended for long-term reliability. For sustained operation, keep shunt current between 60µA and 15mA - the device is fully characterized and guaranteed within this range. Exceeding 20mA risks permanent junction damage even for brief transients.

Can MAX6138BEXR50 be used with a 1µF output capacitor without stability issues?

Yes, MAX6138BEXR50 is explicitly designed to remain stable with any output capacitance, including 1µF or larger. The datasheet confirms stability with capacitive loads and shows output impedance curves with CL = 1µF across frequency. This eliminates the need for external compensation and simplifies design in applications like ADC reference buffers where large bypass caps are standard.

What does the "B" in MAX6138BEXR50 indicate regarding accuracy and temperature performance?

The "B" denotes the 0.2% initial accuracy grade (MAX6138B) - meaning its 5.000V output is guaranteed between 4.990V and 5.010V at +25°C. Its temperature coefficient remains ≤25ppm/°C over –40°C to +85°C regardless of grade. The "B" grade offers tighter tolerance than "C" (0.5%) while costing less than "A" (0.1%), making it ideal for applications needing better-than-standard accuracy without premium pricing.

Is Pin 3 of MAX6138BEXR50 required to be connected, and if so, how?

Pin 3 is labeled N.C. (No Connection) and must either be left floating or connected directly to Pin 2 (–). The datasheet explicitly states "PIN 3 MUST BE LEFT FLOATING OR CONNECTED TO PIN 2." Leaving it unconnected is acceptable and common in layout; tying it to Pin 2 adds no functional benefit but avoids potential floating-node coupling. Never connect Pin 3 to any other net - doing so may compromise regulation or cause parametric shift.

How does MAX6138BEXR50 compare to the LM4040 in terms of size, accuracy, and thermal performance?

MAX6138BEXR50 is 50% smaller (SC70-3 vs. SOT23-3), offers up to 5× better initial accuracy (0.2% vs. 1.0% for LM4040C), and has half the temperature coefficient (25ppm/°C vs. 50–100ppm/°C). It also achieves lower noise (80µVRMS vs. >120µVRMS) and guarantees stability with capacitive loads - whereas LM4040 typically requires an external capacitor. These advantages make MAX6138BEXR50 a higher-performance, drop-in replacement in space- and precision-critical designs.